1. Field of the Invention
The present invention relates to a carrier-attached copper foil, a laminate, a method for producing a printed wiring board, and a method for producing an electronic device.
2. Description of Related Art
A printed wiring board is typically produced through processes that involve bonding an insulating substrate to a copper foil to produce a copper-clad laminated board, and forming a conductor pattern by etching the copper foil surface. As miniaturization of electronic devices continues and the need for higher performance increases, there has been progress in the development of a high-density mounting technique for mounting components, and a technique for achieving high signal frequency. This has created new requirements for printed wiring boards, including fine (fine pitch) conductor patterns, or accommodation of high frequencies.
In order to meet the fine pitch requirement, a copper foil having a thickness of 9 μm or less, or a smaller thickness as thin as 5 μm or less is needed. Such ultrathin copper foils have poor mechanical strength, and easily break or produce wrinkles during production of a printed wiring board, and there has been an emergence of a carrier-attached copper foil that uses a thick metal foil as a carrier, and in which an ultrathin copper layer is electrodeposited on the carrier via a release layer. The ultrathin copper layer is laminated to an insulating substrate, and, after the thermocompression of these two layers, the carrier is released and removed via the release layer. A fine circuit is formed by using a technique (MSAP: Modified-Semi-Additive-Process) that etches and removes the ultrathin copper layer with a sulfuric acid-hydrogen peroxide-based etchant after forming a circuit pattern with a resist on the exposed surface of the ultrathin copper layer.
The resin bonding surface of the ultrathin copper layer in the carrier-attached copper foil mainly needs to have sufficient peel strength between the ultrathin copper layer and the resin base, and the peel strength needs to be sufficiently remain even after treatments and processes, such as high-temperature heating, wet processes, soldering, and chemical treatments. In a typical method of improving the peel strength between the ultrathin copper layer and the resin base, large numbers of roughening particles are attached to the ultrathin copper layer after creating a large surface profile (irregularities, roughness) on the ultrathin copper layer.
However, a problem occurs when such an ultrathin copper layer having a large profile (irregularities, roughness) is used for a semiconductor package substrate, which requires a particularly fine circuit pattern compared to other printed wiring boards. Specifically, unwanted copper particles remain after etching the circuit, and this causes problems such as insulation failure between circuit patterns.
WO2004/005588 discloses a carrier-attached copper foil for fine circuits, including semiconductor package substrates. Specifically, this publication attempts to use a carrier-attached copper foil that is produced without roughening a surface of an ultrathin copper layer. Because of its low profile (irregularities, degree of roughness, roughness), the unroughened ultrathin copper layer tends to have poorer adhesion (peel strength) for resin than a common copper foil for printed wiring boards. This carrier-attached copper foil thus needs further improvements.
The previous efforts to develop a carrier-attached copper foil had a primary focus on the peel strength between an ultrathin copper layer and a resin base. For this reason, there are not many studies concerning a carrier-attached copper foil that is desirable for fine circuit formation and suited for high-density mounting on a printed wiring board, and there is a room for further improvements.